Hydromechanical transmission and warm-up method

ABSTRACT

Methods and systems for a hydromechanical transmission are provided. In one example, the method includes responsive to rotation of a portion of a mechanical assembly induced by cranking of an engine, blocking an output shaft of the hydromechanical transmission via joint engagement of a forward drive clutch and a reverse drive clutch. The method further includes pressurizing a hydrostatic assembly while the forward drive clutch and the reverse drive clutch remain jointly engaged, where the mechanical assembly is coupled in parallel with the hydrostatic assembly.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority to U.S. Provisional ApplicationNo. 63/169,146, entitled “HYDROMECHANICAL TRANSMISSION AND WARM-UPMETHOD”, and filed on Mar. 31, 2021. The entire contents of theabove-listed application are hereby incorporated by reference for allpurposes.

TECHNICAL FIELD

The present disclosure relates to a warm-up procedure for ahydromechanical transmission.

BACKGROUND AND SUMMARY

Hydraulic transmissions, such as hydromechanical variable transmissions(HVTs), rely on hydraulic fluid, such as oil, for many tasks. Thesetasks may include power vector in the hydrostatic units, control ofhydrostatic units and clutches, as well as cooling and lubrication.Certain hydraulic transmissions may be designed to function at aspecific oil viscosity or within a desired range of viscosities. Forexample, some transmission may be operated to maintain the oiltemperature around a set-point temperature or within a desiredtemperature range. When operated outside of the desired temperaturerange, degradation of gearbox components as well as declines in gearboxperformance may occur. The inventors have therefore recognized a desireto more rapidly increase gearbox temperature to avoid componentdegradation and drops in gearbox performance.

The inventors developed a warm-up method for a hydromechanicaltransmission to at least partially resolve the abovementioned issues.The hydromechanical transmission includes a mechanical assembly coupledin parallel with a hydrostatic assembly. The warm-up method includes,during engine cranking, blocking an output of the hydromechanicaltransmission through engagement of a forward drive clutch and a reversedrive clutch in the mechanical assembly. The method further includes,increasing the differential pressure in the hydrostatic assembly viaoperation of a hydraulic pump based on a hydraulic motor speedreference. In this way, the hydrostatic assembly can be rapidlypressurized to increase hydraulic fluid temperature while clutchoperation is coordinated to hold the transmission's output stationary.Therefore, undesired component wear and declines in transmissionperformance occurring during cold start conditions may be efficientlydiminished when compared to previous warm-up strategies.

In one example, the method may further include, prior to blocking theoutput shaft, operating the hydrostatic assembly in a speed control modeto synchronize the forward drive clutch and the reverse drive clutch. Inthis way the clutches may be efficiently readied for output shaftblocking.

Still further, in another example, the method may further includesubsequent to the warm-up (e.g., in anticipation of vehicle launch)switching the hydrostatic unit from the speed control mode to a torquecontrol mode, subsequent to disengagement of the forward drive clutchand reverse drive clutch. In this way, the transmission may transitionbetween speed and torque control modes to achieve desired performancecharacteristics during warm-up and launch, for instance.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic representation of a hydromechanical transmissionsystem in a vehicle.

FIGS. 2 and 3 are examples of control systems for a hydrostatic assemblyin a hydromechanical transmission.

FIGS. 4-8 depict a warm-up sequence for the hydromechanical transmissionsystem, illustrated in FIG. 1 .

FIG. 9 is a method for operation of a hydromechanical transmission.

DETAILED DESCRIPTION

FIG. 1 shows a schematic depiction of a transmission system 100 with ahydromechanical transmission 101 (e.g., a hydromechanical variabletransmission) in a vehicle 102 or other suitable machine platform. Inone example, the vehicle may be an off-highway vehicle, although thetransmission may be deployed in on-highway vehicles, in other examples.An off-highway vehicle may be a vehicle whose size and/or maximum speedprecludes the vehicle from being operated on highways for extendeddurations. For instance, the vehicle's width may be greater than ahighway lane and/or the vehicle top speed may be below the highwaysmaximum allowable speed, for example. Industries and their correspondingoperating environments in which the vehicle may be deployed includeforestry, mining, agriculture, etc. In either case, the vehicle may bedesigned with auxiliary systems driven by hydraulic and/or mechanicalpower take-offs (PTOs).

The transmission system 100 may function as an infinitely variabletransmission (IVT) where the transmission's gear ratio is controlledcontinuously from a negative maximum speed to a positive maximum speedwith an infinite number of ratio points. In this way, the transmissioncan achieve a comparatively high level of adaptability and efficiencywhen compared to transmission which operate in discrete ratios.

The transmission system 100 may have asymmetric maximum output speedsfor forward and reverse direction. This forward-reverse speed asymmetrymay enable the transmission to achieve a desired breadth of speedranges. However, other suitable output speed variations have beencontemplated, such as symmetric output speeds in the forward and reversedirections, which may however, increase system complexity through theuse of an additional clutch.

The transmission system 100 may include or receive power from a motivepower source 104 such as an engine, an electric motor (e.g., an electricmotor generator), combinations thereof, and the like. As such, in oneexample, both and internal combustion engine and an electric motor maybe rotationally coupled to the transmission system 100 in a hybridconfiguration. In other examples, the vehicle may be a battery electricvehicle (BEV) where the power source for the transmission is an electricmotor-generator.

A power source disconnect clutch 106 may be further provided in thetransmission. The disconnect clutch 106 is configured to couple anddecouple the power source 104 from the transmission. The disconnectclutch 106, as well as the other disconnect clutches described herein,may be dog clutches, in one example, or friction clutches, in otherexamples. Gears 108, 110, such as bevel gears, may be used torotationally couple the power source 104 to an input shaft 112. Asdescribed herein, a gear may be a mechanical component which rotates andincludes teeth that are profiled to mesh with teeth in one or morecorresponding gears to form a mechanical connection that allowsrotational energy transfer therethrough.

A mechanical PTO 114 may be coupled to the input shaft 112. Themechanical PTO 114 may drive an auxiliary system such as a pump (e.g., ahydraulic pump, a pneumatic pump, and the like), a winch, a boom, a bedraising assembly, and the like. To accomplish the power transfer toauxiliary components, the PTO may include an interface, shaft(s),housing, and the like. However, in other examples, the PTO and/or thedisconnect clutch may be omitted from the transmission system. A gear116 may be coupled to the input shaft 112. A mechanical assembly 118 isfurther included in the transmission system 100. The mechanical assembly118 may include the shaft 112 and/or the gear 116 as well as shaft 167,described in greater detail herein. Further, the transmission mayinclude a shaft 120 and a gear 122 rotationally coupled to the gear 116on the input shaft 112. Dashed line 124 and the other dashed linesdepicted in FIG. 1 indicate a mechanical connection between componentswhich facilitates rotational energy transfer therebetween.

A gear 126 meshing with gear 122 may be rotationally attached to acharging pump 128. The charging pump 128 may be designed to deliverpressurized fluid to hydraulic components in the transmission such as ahydraulic motor 134 (e.g., hydrostatic motor), a hydraulic pump 136(e.g., hydrostatic pump), and the like. The fluid pressurized by thecharging pump may additionally be used for clutch actuator and/ortransmission lubrication. The charging pump may include a piston, arotor, a housing, chamber(s), and the like to allow the pump to movefluid. The mechanical assembly 118 is rotationally coupled in parallelto a hydrostatic assembly 130 (e.g., a hydrostatic unit). Further, thehydrostatic assembly 130 may have a U-shape design where the shafts 131,133 serve as a mechanical interface for the hydraulic pump 136 (e.g.,variable displacement pump) and the hydraulic motor 134 (e.g., fixedbent axis motor), respectively, are parallel to one another and arrangedon one side of the assembly. This U-shaped layout permits thehydrostatic assembly's size to be reduced and enables the use of highpressure hoses to be forgone to reduce manufacturing costs as well thechance of hydrostatic unit degradation, if desired. Still further, thehydrostatic assembly 130 may be arranged on an opposite side of thetransmission as the charging pump 128 and/or axially offset fromclutches 170, 172. Arranging the hydrostatic assembly in this mannerpermits the width and length of the transmission to be reduced andallows the installation of the transmission in the vehicle to besimplified. Further, the motor and the pump in the hydrostatic assemblymay be enclosed a common housing to increase transmission compactness.

The mechanical assembly 118 is rotationally coupled in parallel to ahydrostatic assembly 130. The coupling of the hydrostatic assembly tothe mechanical assembly enables the transmission to achieve power splitfunctionality in which power may synchronously flow through either pathto additively combine or recirculate power through the system. Thispower split arrangement allows the transmission's power flow to behighly adaptable to increase efficiency over a wide range of operatingconditions. Thus, the transmission may be a full power splittransmission, in one example.

The mechanical assembly 118 may include multiple mechanical paths thatare coupled in parallel to the hydrostatic assembly. To elaborate, theshaft 167 may serve as a junction for a first mechanical path (e.g.,branch) 119 and a second mechanical path (e.g., branch) 121. Toelaborate, the first mechanical path 119 may provide rotational energytransfer capabilities from an interface of the hydrostatic assembly 130to a ring gear 158 of a first planetary gearset 148, during certainoperating conditions. Additionally, the second mechanical path 121 mayprovide rotational energy transfer capabilities from the interface ofthe hydrostatic assembly 130 to a carrier 160 of a second planetarygearset 150. Arranging the mechanical paths in this manner may allow thetransmission to efficiently achieve a desired range of gear ratios.

A disconnect clutch 132 may be arranged between the hydrostatic assembly130 and the shaft 120. The disconnect clutch 132 is configured torotationally couple and decouple the mechanical assembly 118 from thehydrostatic assembly 130. To elaborate, the disconnect clutch may be adog clutch, in one example.

The hydrostatic assembly 130 includes a hydraulic motor 134 (e.g.,hydrostatic motor) and a hydraulic pump 136 (e.g., hydrostatic pump).Further, the hydraulic pump 136 may include a first mechanical interface138 and a second mechanical interface 140. The first mechanicalinterface 138 may be rotationally coupled to the disconnect clutch 132and the second mechanical interface 140 may be rotationally coupled toanother mechanical PTO 142. Again, the mechanical PTO may be used todrive an auxiliary vehicle system such as an air compressor, amechanical arm or boom, an auger, etc. In this way, the transmission maybe adapted for a variety of end-use operating environments.Specifically, providing multiple PTOs, in the arrangement depicted inFIG. 1 , enables the transmission system to meet end-use design goals ina variety of different types of vehicles, if wanted. As such, thesystem's applicability is expanded and the customer appeal of thetransmission is increased.

The hydraulic pump 136 may be a variable displacement bi-directionalpump, in one example. Specifically, the pump may be an axial pistonpump, in one instance. To elaborate, the axial piston pump may include aswash plate that interacts with pistons and cylinders to alter thepump's displacement via a change in swivel angle, in one specificexample. However, other suitable types of variable displacementbi-directional pumps have been contemplated.

The hydraulic motor 134 may be a fixed displacement bi-directional motor(e.g., fixed bent axis motor). The fixed bent axis motor is relativelycompact when compared to variable displacement motors. The system cantherefore achieve greater space efficiency and pose less spaceconstraints on other systems in the vehicle, if desired. However,alternate types of pumps and/or motors may be used, if motoradjustability is favored at the expense of compactness. For instance,the hydraulic motor may be a variable displacement motor.

Hydraulic lines 144, 146 are attached to hydraulic interfaces in each ofthe motor and pump to enable the hydrostatic assembly to provideadditive and power circulation functionality with regard to themechanical branches arranged in parallel with the hydrostatic assembly130. For example, in an additive power mode, power from both thehydrostatic and mechanical assemblies is combined at one of theplanetary gearsets and delivered to the transmission output. In a powersplit mode, power is recirculated through the hydrostatic assembly.Therefore, the hydraulic pump 136 and the hydraulic motor 134 may beoperated to flow power to the sun gears of either planetary assemblyfrom the hydraulic motor, during certain conditions. Conversely, duringother conditions, the hydraulic pump 136 and the hydraulic motor 134 maybe operated to flow power back to the gearset and the mechanicalbranches.

The transmission system 100 further includes the first planetary gearset148 and the second planetary gearset 150. The first planetary gearset148 may include a carrier 152 on which planet gears 154 rotate. Theplanet gears 154 may mesh with a sun gear 156 and the ring gear 158.Likewise, the second planetary gearset 150 may include the carrier 160,planet gears 162, a sun gear 164, and a ring gear 166. Therefore, thesecond planetary gearset 150 may again be a simple planetary gear.Further, bearings arranged between the planet gears and the carrier ineach planetary arrangement may facilitate rotation thereof. The sungears and/or shafts to which they are attached may further have bearingscoupled thereto. The bearings may be roller bearings (e.g., needleroller bearings), ball bearings, or other suitable types of bearingsthat enable component rotation while constraining other relativemotions.

The carrier 160 of the second planetary gearset 150 may be rotationallycoupled to the ring gear 158 of the first planetary gearset 148.Further, the carrier 160 of the second planetary gearset 150 may berotationally coupled to a shaft 167. The shaft 167 may extend through acentral opening in an extension 186, described in greater detail herein.This rotational attachment scheme may be conceptually described as aformation of mechanical branches attached in parallel to the hydrostaticassembly 130.

As described herein a parallel attachment between components,assemblies, etc., denotes that the input and output of the twocomponents or grouping of components are rotationally coupled to oneanother. This parallel arrangement allows power to recirculate throughthe hydrostatic assembly, during some conditions, or be additivelycombined from the mechanical and hydrostatic branches, during otherconditions. As a result, the transmission's adaptability is increased.

The sun gears 156, 164 of the first and second planetary gearsets 148,150 may be rotationally coupled (e.g., directly attached) to oneanother. Attaching the sun gears in this manner may enable thetransmission to achieve a desired gear ratio, compactness, andefficiency.

The hydraulic motor 134 may be rotationally coupled to the sun gear 156via another disconnect clutch 168 that is designed to rotationallyconnect and disconnect the motor from the planetary gearset 148. Thedisconnect clutch may be a dog type clutch which uses an interferencefit between component for clutch engagement, in one example. However, inan alternate example, the disconnect clutch may be another suitable typeof clutch, such as a friction clutch.

The transmission system 100 further includes a reverse clutch 170, afirst forward drive clutch 172, and a second forward drive clutch 174.More generally, the first forward drive clutch may be referred to as afirst clutch or a first forward clutch, the reverse drive clutch may bereferred to as a second clutch or a reverse clutch and the secondforward drive clutch may be referred to as a third clutch or a secondforward clutch. Further, the first forward drive clutch 172 and thereverse clutch 170 may be coaxially arranged.

The clutches 170, 172, 174 may be friction clutches that each includeplates, spacers, and the like. These clutch plates may rotate about acommon axis and are designed to engage and disengage one another tofacilitate selective power transfer to downstream components. In thisway, the clutches may be closed and opened to place them in engaged anddisengaged states. In the disengaged state, power does not pass throughthe clutch. Conversely in the engaged state, power travels through theclutch during transmission operation. Further, the clutches may behydraulically, electromagnetically, and/or pneumatically actuated. Forinstance, the clutches may be adjusted via a hydraulic piston. Theadjustability may be continuous, in one example, where the clutch may betransition through partially engaged states to a fully engaged state,where a relatively small amount of power loss occurs in the clutch.However, in other examples, the clutches may be discretely adjusted.

The carrier 152 may include an extension 175 with a gear 176 that mesheswith a gear 177. The gear 177, in the illustrated example, isrotationally coupled to the reverse clutch 170 and the first forwardclutch 172. The reverse clutch 170 and the first forward clutch 172 areshown arranged adjacent to one another and may share a common rotationalaxis. Because of this proximal clutch arrangement, the system mayexhibit greater compactness which poses less space constraints onadjoining vehicle systems. Alternatively, the reverse clutch may bespaced away from the first forward clutch which may, however, decreasesystem compactness.

A gear 179 may reside on an output shaft 180 of the reverse clutch 170.Likewise, a gear 181 may reside on an output shaft 182 of the firstforward clutch 172. Both gears 179, 181 may be rotationally attached toa system output shaft 171 via gears 183, 184 respectively. In this way,both the reverse clutch and the first forward clutch deliver power tothe transmission's output, during different operating conditions.

The system output shaft 171 may include one or more interfaces 185(e.g., yokes, gears, chains, combinations thereof, and the like). Theoutput shaft is specifically illustrated with two outputs. However, thetransmission may include an alternate numbers of outputs. The gear 179is rotationally coupled to the output shaft via meshing with gear 183.Arrows 191 depict the flow of power from the transmission system todrive axles 192 and/or other suitable downstream vehicle components orvice versa. A driveline with a shaft, joints, and the like may be usedto carry out the power transfer between the transmission and the axles.It will be understood that the drive axles may include drive wheels.

A parking brake mechanism 141 designed to engage and disengage theoutput interfaces 185 may further be included in the hydromechanicaltransmission 101. The parking brake mechanism 141 may include calipers,drums, and other suitable components for the prevention of rotation ofthe transmission's output. The parking brake mechanism 141 may bemechanically and/or hydraulically actuated.

The ring gear 166 of the second planetary gearset 150 may include theextension 186 with a gear 187 position thereon. The gear 187 may berotationally attached to a gear 188 in the second forward clutch 174, asindicated via a dashed line. The gear 188 may be coupled to a first setof plates in the clutch 174. A second set of plates in the clutch may beattached to an output shaft 189 and a gear 190. The gear 190 may berotationally coupled to the gear 183, as indicated by a dashed line. Dueto the arrangement of the clutches and the planetary gearsets, thetransmission system 100 achieves a higher efficiency and enhanceddrivability, comfort, and productivity than previous hydromechanicaltransmissions.

The transmission system 100 may additionally include a lubricationsystem and hydraulic control system which may include a sump. Thislubrication system may further include conventional components forlubricating the gears and/or the clutches such as pumps, conduits,valves, and the like.

A control system 193 with a controller 194 may further be incorporatedin the transmission system 100. The controller 194 includes a processor195 and memory 196. The memory 196 may hold instructions stored thereinthat when executed by the processor cause the controller 194 to performthe various methods, control strategies, etc., described herein. Theprocessor 195 may include a microprocessor unit and/or other types ofcircuits. The memory 196 may include known data storage mediums such asrandom access memory, read only memory, keep alive memory, combinationsthereof, etc.

The controller 194 may receive vehicle data and various signals fromsensors positioned in different locations in the transmission system 100and/or the vehicle 102. The sensors may include gear speed sensors 197,198, 199 which detect the speed of gear 116, gear 184, and gear 176,respectively. In this way, gear speed at the input and the output of thesystem may be detected along with the gear speed at the output of thefirst planetary gearset 148. However, in other examples, the speeds ofat least a portion of the gears may be modeled by the controller. Thevehicle may further include a torque sensor 155. Alternatively, thetorque and/or speed of the output shaft may be modeled.

The controller 194 may send control signals to an actuator in thehydraulic pump 136 or an actuation system coupled to the pump to adjustthe pump's output and/or direction of hydraulic fluid flow.Additionally, the clutches 170, 172, 174 may receive commands (e.g.,opening or closing commands) from the controller and actuators in theclutches or actuation systems coupled to the clutches may adjust thestate of the clutch in response to receiving the command. For instance,the clutches may be actuated via hydraulically controlled pistons,although other suitable clutch actuators have been envisioned. The othercontrollable components in the transmissions system include thehydraulic motor 134, the clutch 106, the clutch 132, the clutch 168, themotive power source 104, and the like. These controllable components mayfunction similarly with regard to receiving control commands andadjusting an output and/or a state of a component responsive toreceiving the command via an actuator. Additionally or alternatively, avehicle electronic control unit (ECU) may be provided in the vehicle tocontrol the power source (e.g., engine and/or motor). Furthermore, thecontrol system 193 and specifically the controller 194 with the memory196 and processor 195 may be configured to carry out the warm-upstrategy expanded upon herein with regard to FIGS. 4-8 .

The transmission system 100 may include input devices 149, 151 (e.g., adrive-input device (e.g., drive pedal), brake-input device (e.g., brakepedal), gear selector, and the like). The input device 151, responsiveto driver input, may generate a power request. Further, the transmissionsystem may automatically switch between drive modes when demanded. Toelaborate, the operator may request a forward or reverse drive modespeed change, and the transmission may increase speed and automaticallytransition between the drive ranges associated with the different drivemodes, when needed. Further, in one example, the operate may requestreverse drive operation while the vehicle is operating in a forwarddrive mode. In such an example, the transmission may automaticallyinitiate a shift (e.g., synchronous shift) between the forward andreverse drive modes. In this way, the operator may more efficientlycontrol the vehicle, in comparison to transmissions designed for manualdrive mode adjustment. However, in other examples, the system may bedesigned to allow the vehicle operator to manually request a mode changebetween the forward drive ranges, for instance. It will further beappreciated, that the power source may be controlled in tandem with thetransmission. For instance, when power request requested is received bythe controller, the power source's output speed may be correspondinglyincreased.

The hydromechanical transmission 101 shown in FIG. 1 may be operated indifferent drive ranges (e.g., a reverse drive range, a first forwarddrive range, and a second forward drive range). In each of the driveranges power flow through the hydrostatic assembly may be additive orcirculatory to provide continuous range adjustment. To elaborate, thepump's displacement may be adjusted within each drive range to achievedifferent speed ratios. Specifically, in one example, the first forwarddrive range may be entered by engaging the first forward drive clutch172 and disengaging and/or sustaining disengagement of the otherclutches 170, 174. Entry into the other drive ranges may occur in asimilar manner. For instance, the second forward drive range may beimplemented by engaging the second forward drive clutch 174 anddisengaging and/or sustaining disengagement of the clutches 170, 172.Further, the hydromechanical transmission 101 may be placed in a blockedcondition by simultaneously engaging the first forward drive clutch 172and the reverse clutch 170. Specifically, in one example, if thetransmission output speed is null and the hydrostatic pump displacementis approaching an upper displacement (e.g., maximum displacement) thenboth the first forward clutch and the reverse clutch differential speedsare approximately zero and can therefore be closed for clutch blocking.

An axis system with an x-axis, y-axis, and z-axis is provided in FIGS. 1and 4-8 . The x-axis may be a lateral axis, the y-axis may be alongitudinal axis, and the z-axis may be parallel to a gravitationalaxis, although numerous orientations of the axes are possible.

FIG. 2 shows a control system 200 for a hydrostatic assembly 202 with ahydraulic pump 204 and a hydraulic motor 206. The hydrostatic assembly202 is an example of the hydrostatic assembly 130, depicted in FIG. 1 ,and redundant description is therefore omitted for concision.

A hydraulic control piston 208 that is designed to control the swashplate angle of the hydraulic pump 204 is further included in the controlsystem 200. A first pressure control valve 210 and a second pressurecontrol valve 212 are in fluidic communication with the hydrauliccontrol piston 208. Specifically, the pressure control valves are influidic communication with chambers on opposing sides of the piston. Assuch, varying the pressure in the chambers changes the piston'sposition. Further, adjustment of the hydraulic control piston 208 altersthe swash plate angle of the hydraulic pump 204. Lines 250 represent thehydraulic connection between the pressure control valves 210, 212 andthe hydraulic control piston 208.

Further in the control system, a pressure control function 214 in acontroller provides current to the first and second pressure controlvalves 210, 212. The pressure control function 214 may be stored asinstructions in memory of a controller such as the controller 194,described above with regard to FIG. 1 . The pressure control function214 receives inputs from pressure sensors 216, 218 designed to sense thepressure in hydraulic lines 220, 222, respectively. Lines 252, 254represent the transfer of electronic signals between the pressuresensors 216, 218 and the pressure control function 214 as well as thetransfer of control signals from the pressure control function to thepressure control valves 210, 212.

The control system 200 may be used during a transmission warm-upstrategy to increase the pressure differential in the hydrostaticassembly 202. High pressure in the hydrostatic unit will provide astrong increase in power losses, significantly increasing the heatgeneration inside the gearbox. Specifics of the warm-up strategy arediscussed in greater detail herein with regard to FIGS. 4-8 .

FIG. 3 depicts another control system 300 for the hydrostatic assembly202 with the hydraulic pump 204 and the hydraulic motor 206. The controlsystem 300 again includes the first and second pressure control valves210, 212 that deliver pressurized fluid (e.g., oil) to chambers of thehydraulic control piston 208. It will be understood, that both controlsystems shown in FIGS. 2-3 may be used in the transmission system 100,depicted in FIG. 1 . Redundant description of the overlapping controlsystem components is omitted for brevity.

The control system 300 further includes a motor speed control function302 that supplies current to the pressure control valves 210, 212. Themotor speed control function 302 may be a software module stored inmemory of a controller. The motor speed control function 302 may usedesired motor speed 304 and sensed motor speed 306 as inputs. The motorspeed 306 may be transferred from a motor speed sensor 308 coupled tothe hydraulic motor 206. On the other hand, the desired motor speed 304may be determined by a desired motor speed calculation module 310 whichuses an engine speed 312 as an input.

The control system 300 may implement a warm-up approach by controllingthe speed of the hydraulic motor 206 using pump displacement control.The desired speed may be automatically calculated based on the enginespeed. A speed control function may provide the desired control currentin valves 210, 212 to obtain the desired pump displacement whichcorresponds to the desired motor speed. The hydrostatic assembly may beoperated in the speed control mode to synchronize clutches in thetransmission, such as the forward and reverse clutches.

FIGS. 4-8 show a warm-up sequence for the transmission system 100 withthe hydromechanical transmission 101. A rapid warm-up is achieved byincreasing the pressure in the hydrostatic assembly 130. This elevatedpressure correspondingly increases power losses and therefore increasesheat generation in the transmission. It will be understood that thewarm-up sequence depicted in FIGS. 4-8 is applicable to othertransmissions that include at least one planetary gearset and at leasttwo speed/torque sources.

Turning specifically to FIG. 4 , a first step in the warm-up sequencewhere the motive power source 104 (e.g., engine) is off is depicted. Assuch, the hydrostatic assembly 130 is depressurized and the mechanicalassembly 118 is substantially stationary. Next, as illustrated in FIG. 5, cranking of the motive power source 104 initiates rotation of aportion of the mechanical assembly 118 and specifically the chargingpump 128. In this way, the oil pressure in the transmission begins toincrease. The mechanical power path during engine cranking is indicatedat 500. Cranking of the engine may involve rotating the engine using astarter motor, for instance. Responsive to engine cranking, the carrier160, the ring gear 158, and the shaft 120 in the mechanical assembly 118begin to rotate.

As shown in FIG. 6 , the rotation of the output shaft 171 is inhibitedthrough operation of the parking brake mechanism 141 as indicated at600. While the parking brake mechanism 141 is engaged, the motive powersource 104 continues to crank and induce rotation of the carrier 160,the ring gear 158, and the shaft 120 in the mechanical assembly 118 asindicated via mechanical power path 602. In FIG. 6 , the charging pump128 continues to receive rotational input and therefore increase in oilpressure continues while the parking brake mechanism blocks rotation ofthe output shaft 171.

Next in the warm-up sequence, the hydrostatic assembly 130 is operatedusing a speed control function to achieve a desired motor speedset-point as shown in FIG. 7 . For instance, the hydrostatic assemblymay be operated using the control strategy depicted in FIG. 3 .Operating the hydrostatic assembly in a speed control mode permitssynchronization of the first forward drive clutch 172 and the reversedrive clutch 170. Further during this portion of the warm-up the parkingbrake mechanism continues to block movement of the output shaft 171 asindicated at 704. The mechanical power path 700 and the hydraulic powerpath 702 during this portion of the warm-up sequence are depicted inFIG. 7 . As such, charging pump 128 continues to increase the pressureof the oil.

Once the clutches are synchronized, the clutches 170, 172 are engaged toplace the transmission's output in a blocked condition, as shown at 800in FIG. 8 . Once the clutch blocking is achieved, the parking brakemechanism 141 may be released, if desired. However, in another example,parking brake engagement may be sustained. Subsequently, the hydrostaticassembly 130 is operated to increase the hydraulic pressure and reach athreshold temperature for the hydraulic fluid to initiate vehiclelaunch. The mechanical power path 802 and the hydraulic power path 804through the transmission during this portion of warm-up are furthershown in FIG. 8 . In FIG. 8 the speed control of the hydraulic motor 136may persist until vehicle launch is desired. During launch, thehydrostatic unit may be switched from the speed control mode to a torquecontrol mode, where the hydraulic unit is controlled to follow a torqueset-point of the motor. Conversely, in the speed control mode, thehydraulic unit is controlled to follow a speed set-point. Further,during launch the blocking condition of the clutches 170, 172 may bereleased. For instance, the reverse clutch may be release to allow thetransmission to propel the vehicle in a forward drive direction.Switching from the speed control mode to the torque control mode in thismanner enable the transmission's performance to be enhanced.

FIG. 9 shows a method 900 for operation of a hydromechanicaltransmission. The method 900 may be carried out by the transmissionsystems and components described above with regard to FIGS. 1-8 , in oneexample. However, in other examples, the method 900 may be implementedusing other suitable transmission systems and components. Further, themethod may be carried out as instructions stored in memory executed by aprocessor in a controller. As such, performing the method steps mayinclude receiving inputs from sensors and sending and/or receivingcommands which trigger adjustment of associate components usingactuators, as previously indicated.

At 901, the method includes cranking the engine. For instance, a startermotor may be used to crank the engine. Next at 902, the method includesdetermining operating conditions. The operating conditions may includeengine speed, input device position (e.g., accelerator or brake pedalposition), shift selector position, vehicle speed, and the like. Theoperating conditions may be ascertained via sensor inputs and/ormodeling.

At 904, the method judges whether or not to initiate an engine warm-upsequence. This engine warm-up judgement may take into account inputdevice position (e.g., accelerator pedal position, brake pedal positon,key position, and the like). For instance, the method may judge thatwarm-up should be initiated responsive to key-on and vice-versa.

If it is determined that warm-up should not be initiated (NO at 904) themethod moves to 906 where the method includes maintaining the currenttransmission control strategy. For instance, the hydromechanicaltransmission may remain shut-down along with the engine in thepowertrain.

Conversely, if it is determined that a warm-up sequence should beinitiated (YES at 904) the method advances to 908 where the methodincludes engaging the parking brake to prevent rotation of thetransmission's output shaft. For instance, the parking brake may bemechanically or hydraulically actuated via the controller. As such, step908 may be automatically implemented. Alternatively, step 908 may beautomatically implemented after engine cranking and prior to decisionblock 904. In such an example, the parking brake engagement may besustained at step 908.

At 910, the method includes implementing speed control of the hydraulicmotor. For example, the hydraulic pump's displacement may be adjusted tofollow a target hydraulic motor speed reference. Specifically, afeedback control strategy may be used where the pump's displacement isadjusted using a control function that measures the deviation of thedesired motor speed with a detected motor speed. The clutch maytherefore be prepared for subsequent clutch blocking.

At 912, the method includes simultaneously engaging the first forwardclutch and the reverse clutch to block the transmission's output. Inthis way, the clutches may be jointly closed to hold the transmission'soutput stationary. It will be appreciated that the method may furtherinclude sustaining engagement of the parking brake mechanism duringengagement of the forward and reverse clutches. The parking brakeengagement may be sustained subsequent to clutch engagement, in oneexample. In this way, the likelihood of unintended vehicle movement maybe decreased due to the redundant braking of the transmission output.Alternatively, the parking brake may be disengaged subsequent toengagement of the forward and reverse clutches.

At 914, the method includes controlling the hydrostatic unit to achievea desired pressure and oil temperature. Specifically, in one example,the hydrostatic unit may switch from speed control to torque controlwhere the hydraulic motor is controlled to achieve a target oilpressure. In this way, transmission performance may be increased. Once atemperature set-point is reached, the hydrostatic unit may transitionfrom the speed control mode to a torque control mode and vehicle launchmay be initiated. Method 900 permits the fluid in the hydromechanicaltransmission to be rapidly warmed thereby increasing transmissionlongevity and reducing the likelihood of component degradation due tolow oil temperatures.

The technical effect of the hydromechanical transmission systems andmethods described herein is to decrease transmission warm-up time, whencompared to previous warm-up methods, which decreases component wear andenhances transmission performance during cold vehicle starts, forinstance.

FIGS. 1 and 4-8 show example configurations with relative positioning ofthe various components. If shown directly contacting each other, ordirectly coupled, then such elements may be referred to as directlycontacting or directly coupled, respectively, at least in one example.Similarly, elements shown contiguous or adjacent to one another may becontiguous or adjacent to each other, respectively, at least in oneexample. As an example, components laying in face-sharing contact witheach other may be referred to as in face-sharing contact. As anotherexample, elements positioned apart from each other with only a spacethere-between and no other components may be referred to as such, in atleast one example. As yet another example, elements shown above/belowone another, at opposite sides to one another, or to the left/right ofone another may be referred to as such, relative to one another.Further, as shown in the figures, a topmost element or point of elementmay be referred to as a “top” of the component and a bottommost elementor point of the element may be referred to as a “bottom” of thecomponent, in at least one example. As used herein, top/bottom,upper/lower, above/below, may be relative to a vertical axis of thefigures and used to describe positioning of elements of the figuresrelative to one another. As such, elements shown above other elementsare positioned vertically above the other elements, in one example. Asyet another example, shapes of the elements depicted within the figuresmay be referred to as having those shapes (e.g., such as being circular,straight, planar, curved, rounded, chamfered, angled, or the like).Additionally, elements co-axial with one another may be referred to assuch, in one example. Further, elements shown intersecting one anothermay be referred to as intersecting elements or intersecting one another,in at least one example. Further still, an element shown within anotherelement or shown outside of another element may be referred as such, inone example. In other examples, elements offset from one another may bereferred to as such.

The invention will be further described in the following paragraphs. Inone aspect, a method for operation of a hydromechanical transmission isprovided. The method includes responsive to rotation of a portion of amechanical assembly induced by rotation of an engine or motor coupled tothe hydromechanical transmission, blocking an output shaft of thehydromechanical transmission via joint engagement of a forward driveclutch and a reverse drive clutch, wherein the mechanical assembly iscoupled in parallel with a hydrostatic assembly; and pressurizing thehydrostatic assembly while the forward drive clutch and the reversedrive clutch remain jointly engaged. In one example, the method mayfurther comprise, prior to blocking the output shaft, operating thehydrostatic assembly in a speed control mode to synchronize the forwarddrive clutch and the reverse drive clutch. In yet another example, themethod may further comprise, prior to joint engagement of the forwarddrive clutch and the reverse drive clutch, engaging a parking brakemechanism coupled to the output shaft; and subsequent to jointengagement of the forward drive clutch and the reverse drive clutch,disengaging the parking brake mechanism.

In another aspect, a hydromechanical transmission is provided thatcomprises a mechanical assembly including a planetary gearset; ahydrostatic assembly coupled in parallel with the mechanical assembly; aforward drive clutch and a reverse drive clutch coupled to themechanical assembly and an output shaft; a controller comprising:instructions that when executed while the mechanical assembly isreceiving rotational input from a motive power source, cause thecontroller to: block the output shaft of the hydromechanicaltransmission via joint engagement of the forward drive clutch and thereverse drive clutch, wherein the mechanical assembly is coupled inparallel with the hydrostatic assembly; and pressurize the hydrostaticassembly while the forward drive clutch and the reverse drive clutchremain jointly engaged.

In yet another aspect, a warm-up method for a hydromechanicaltransmission is provided that comprises responsive to rotation of aportion of a mechanical assembly induced by cranking of an engine,operating a hydrostatic assembly in a speed control mode to synchronizea forward drive clutch and a reverse drive clutch, wherein the forwarddrive clutch and the reverse drive clutch are coupled to the mechanicalassembly and wherein the mechanical assembly is coupled in parallel withthe hydrostatic assembly; blocking an output shaft of thehydromechanical transmission via joint engagement of the forward driveclutch and the reverse drive clutch; and pressurizing the hydrostaticassembly while the forward drive clutch and the reverse drive clutchremain jointly engaged. The method may further comprise, prior to andduring synchronization of the forward drive clutch and the reverse driveclutch, initiating and sustaining engagement of a parking brakemechanism coupled to the output shaft. The method may further comprise,in one example, subsequent to blocking the output shaft, disengaging orsustaining engagement of the parking brake mechanism.

In any of the aspects or combinations of the aspects, the hydrostaticassembly may include a hydraulic pump and a hydraulic motor; andpressurizing the hydrostatic assembly may include operating a hydrauliccontrol piston to adjust displacement of the hydraulic pump.

In any of the aspects or combinations of the aspects, pressurizing thehydrostatic assembly may include increase a pressure differentialbetween hydraulic lines coupled to the hydraulic pump and the hydraulicmotor.

In any of the aspects or combinations of the aspects, the controller maycomprise: instructions that when executed, while the mechanical assemblyis receiving rotational input from the engine or motor, cause thecontroller to: adjust a hydraulic pump in the hydrostatic assembly toachieve a target pump displacement that corresponds to a speed of ahydraulic motor in the hydrostatic assembly.

In any of the aspects or combinations of the aspects, the forward driveclutch and the reverse drive clutch may be coupled to a carrier of theplanetary gearset.

In any of the aspects or combinations of the aspects, the forward driveclutch and the reverse drive clutch may be coaxially arranged.

In any of the aspects or combinations of the aspects, thehydromechanical transmission may further comprise a parking brakemechanism coupled to the output shaft and wherein the controllercomprises: instructions that when executed, prior to the jointengagement of the forward drive clutch and the reverse drive clutch,cause the controller to: engage the parking brake mechanism.

In any of the aspects or combinations of the aspects, the first forwarddrive clutch and the reverse drive clutch may be friction clutches.

In any of the aspects or combinations of the aspects, the first forwarddrive clutch and the reverse drive clutch may be coaxially arranged.

In any of the aspects or combinations of the aspects, the transmissionmay further comprise a second forward drive clutch axially offset fromthe first forward drive clutch.

In any of the aspects or combinations of the aspects, the method mayfurther comprise switching from the speed control mode to a torquecontrol mode subsequent to disengagement of the forward drive clutch andreverse drive clutch.

In any of the aspects or combinations of the aspects, the method mayfurther comprise switching from the speed control mode to a torquecontrol mode subsequent to disengagement of the forward drive clutch andreverse drive clutch.

In any of the aspects or combinations of the aspects, the method mayfurther comprise prior to the joint engagement of the forward driveclutch and the reverse drive clutch, engaging a parking brake mechanismcoupled to the output shaft.

In any of the aspects or combinations of the aspects, the hydrostaticassembly may include a hydraulic pump and a hydraulic motor andpressurizing the hydrostatic assembly may include operating a hydrauliccontrol piston to adjust displacement of the hydraulic pump; andpressurizing the hydrostatic assembly may include increasing a pressuredifferential between hydraulic lines coupled to the hydraulic pump andthe hydraulic motor.

In any of the aspects or combinations of the aspects, the forward driveclutch and the reverse drive clutch may be hydraulically operated andcoaxially arranged.

In another representation, a hydromechanical variable transmission (HVT)is provided that, in one example, comprises a hydrostatic unit coupledin parallel with a mechanical branch that includes a planetary gearsetcoupled to coaxially arranged forward and reverse drive clutches. TheHVT further includes a controller that comprises instructions that whenexecuted, during cranking of an engine coupled to the mechanical branch,cause the controller to synchronously engage the forward and reversedrive clutch and increase a pressure differential in the hydrostaticunit via adjustment of a displacement of a hydrostatic pump in thehydrostatic unit.

Note that the example control and estimation routines included hereincan be used with various transmission and/or powertrain configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory and may be carried outby the control system including the controller in combination with thevarious sensors, actuators, and other transmission and/or vehiclehardware. Further, portions of the methods may be physical actions takenin the real world to change a state of a device. The specific routinesdescribed herein may represent one or more of any number of processingstrategies such as event-driven, interrupt-driven, multi-tasking,multi-threading, and the like. As such, various actions, operations,and/or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example examples described herein, but is provided forease of illustration and description. One or more of the illustratedactions, operations and/or functions may be repeatedly performeddepending on the particular strategy being used. Further, the describedactions, operations and/or functions may graphically represent code tobe programmed into non-transitory memory of the computer readablestorage medium in the vehicle and/or transmission control system, wherethe described actions are carried out by executing the instructions in asystem including the various hardware components in combination with theelectronic controller. One or more of the method steps described hereinmay be omitted if desired.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example, and notlimitation nor restriction. It will be appreciated that theconfigurations and routines disclosed herein are exemplary in nature,and that these specific examples are not to be considered in a limitingsense, because numerous variations are possible. For example, the abovetechnology can be applied to powertrains that include different types ofpropulsion sources including different types of electric machines,internal combustion engines, and/or transmissions. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein. It willbe apparent to persons skilled in the relevant arts that the disclosedsubject matter may be embodied in other specific forms without departingfrom the spirit of the subject matter.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. A method for operation of a hydromechanicaltransmission, comprising: responsive to rotation of a portion of amechanical assembly induced by rotation of an engine or motor coupled tothe hydromechanical transmission, blocking an output shaft of thehydromechanical transmission via joint engagement of a forward driveclutch and a reverse drive clutch, wherein the mechanical assembly iscoupled in parallel with a hydrostatic assembly; pressurizing thehydrostatic assembly while the forward drive clutch and the reversedrive clutch remain jointly engaged; and prior to blocking the outputshaft, operating the hydrostatic assembly in a speed control mode tosynchronize the forward drive clutch and the reverse drive clutch. 2.The method of claim 1, further comprising switching from the speedcontrol mode to a torque control mode subsequent to disengagement of theforward drive clutch and reverse drive clutch.
 3. The method of claim 1,wherein: the hydrostatic assembly includes a hydraulic pump and ahydraulic motor; and pressurizing the hydrostatic assembly includesoperating a hydraulic control piston to adjust displacement of thehydraulic pump.
 4. The method of claim 3, wherein pressurizing thehydrostatic assembly includes increasing a pressure differential betweenhydraulic lines coupled to the hydraulic pump and the hydraulic motor.5. A method for operation of a hydromechanical transmission, comprising:responsive to rotation of a portion of a mechanical assembly induced byrotation of an engine or motor coupled to the hydromechanicaltransmission, blocking an output shaft of the hydromechanicaltransmission via joint engagement of a forward drive clutch and areverse drive clutch, wherein the mechanical assembly is coupled inparallel with a hydrostatic assembly; pressurizing the hydrostaticassembly while the forward drive clutch and the reverse drive clutchremain jointly engaged; and prior to the joint engagement of the forwarddrive clutch and the reverse drive clutch, engaging a parking brakemechanism coupled to the output shaft.
 6. A hydromechanicaltransmission, comprising: a mechanical assembly including a planetarygearset; a hydrostatic assembly coupled in parallel with the mechanicalassembly; a first forward drive clutch and a reverse drive clutchcoupled to the mechanical assembly and an output shaft; and a controllercomprising: instructions that when executed, while the mechanicalassembly is receiving rotational input from a motive power source, causethe controller to: block the output shaft of the hydromechanicaltransmission via joint engagement of the first forward drive clutch andthe reverse drive clutch, wherein the mechanical assembly is coupled inparallel with the hydrostatic assembly; and pressurize the hydrostaticassembly while the first forward drive clutch and the reverse driveclutch remain jointly engaged; the transmission further comprising: aparking brake mechanism coupled to the output shaft, and wherein thecontroller further comprises: instructions that when executed, prior tothe joint engagement of the first forward drive clutch and the reversedrive clutch, cause the controller to: engage the parking brakemechanism; and instructions that when executed, subsequent to the jointengagement of the first forward drive clutch and the reverse driveclutch, cause the controller to:  sustain engagement of the parkingbrake mechanism.
 7. The hydromechanical transmission of claim 6, whereinthe controller comprises: instructions that when executed, while themechanical assembly is receiving rotational input from the motive powersource, cause the controller to: adjust a hydraulic pump in thehydrostatic assembly to achieve a target pump displacement thatcorresponds to a speed of a hydraulic motor in the hydrostatic assembly.8. The hydromechanical transmission of claim 6, wherein the firstforward drive clutch and the reverse drive clutch are coupled to acarrier of the planetary gearset.
 9. The hydromechanical transmission ofclaim 6, wherein the first forward drive clutch and the reverse driveclutch are coaxially arranged.
 10. The hydromechanical transmission ofclaim 6, wherein the first forward drive clutch and the reverse driveclutch are friction clutches.
 11. The hydromechanical transmission ofclaim 10, wherein the first forward drive clutch and the reverse driveclutch are coaxially arranged.
 12. The hydromechanical transmission ofclaim 6, further comprising a second forward drive clutch axially offsetfrom the first forward drive clutch.
 13. A warm-up method for ahydromechanical transmission, comprising: responsive to rotation of aportion of a mechanical assembly induced by cranking of an engine,operating a hydrostatic assembly in a speed control mode to synchronizea forward drive clutch and a reverse drive clutch, wherein the forwarddrive clutch and the reverse drive clutch are coupled to the mechanicalassembly and wherein the mechanical assembly is coupled in parallel withthe hydrostatic assembly; blocking an output shaft of thehydromechanical transmission via joint engagement of the forward driveclutch and the reverse drive clutch; and pressurizing the hydrostaticassembly while the forward drive clutch and the reverse drive clutchremain jointly engaged.
 14. The warm-up method of claim 13, furthercomprising: prior to and during synchronization of the forward driveclutch and the reverse drive clutch, initiating and sustainingengagement of a parking brake mechanism coupled to the output shaft. 15.The warm-up method of claim 13, further comprising switching from thespeed control mode to a torque control mode subsequent to disengagementof the forward drive clutch and reverse drive clutch.
 16. The warm-upmethod of claim 13, further comprising: prior to the joint engagement ofthe forward drive clutch and the reverse drive clutch, engaging aparking brake mechanism coupled to the output shaft.
 17. The warm-upmethod of claim 13, wherein: the hydrostatic assembly includes ahydraulic pump and a hydraulic motor; pressurizing the hydrostaticassembly includes operating a hydraulic control piston to adjustdisplacement of the hydraulic pump; and pressurizing the hydrostaticassembly includes increasing a pressure differential between hydrauliclines coupled to the hydraulic pump and the hydraulic motor.
 18. Thewarm-up method of claim 13, wherein the forward drive clutch and thereverse drive clutch are hydraulically operated and coaxially arranged.